1. Field of the Invention
The present invention relates to a cool cathode tube control circuit, wherein a control logic circuit is electrically connected to a regulator control circuit, a lighting circuit, a fine-adjusting control circuit, and an abnormality detecting circuit for receiving the signals of a fine-adjusting setting circuit and the abnormality protecting circuit and process the received signals to output digital signals for driving the pre-stage voltage boost regulator and the lighting circuit of a lighting device. Thereby, the lighting device is driven so that the plurality of lamp tubes are actuated synchronously and have the same illumination.
2. Description of Related Art
The general cool cathode tube lighting device (referring to FIG. 1, only one lighting device is illustrated). The lighting device mainly includes a pre-stage voltage boost regulator 12 for providing a high voltage DC power source and a plurality of lighting circuits 14. Each lighting circuit 14 includes a resonant inductor 142, a resonant capacitor 144 and a transformer circuit 146 for driving the corresponding cool cathode tube 148. To avoid the damage of the system since the over-voltage or over-current occurs due to open circuit or short circuit of abnormal loads. The lighting device can be installed a plurality of abnormal protecting circuits 16 corresponding to each cool cathode tube 148. Thereby, the system is protected from an abnormal load. Besides, to be suitable in various conditions and environments, a fine-adjusting setting circuit 18 may be installed for fine-adjusting the condition of lighting.
However, when the lamp tubes are driven by a general lighting device of a cool cathode tube, the following events will occurs:
1. Variations of temperature induce responses of natural resonant frequencies.
2. Variations of temperature induce responses of the control current of the cool cathode tubes.
3. The variations of the control current of the cool cathode tubes induce responses of natural resonant frequencies.
4. As adjusting the illuminations of a plurality of lamp tubes, the illuminations of the lamp tubes can not be identical and the lighting frequencies thereof can not be identical.
5. The lighting frequency is not identical to that of the pre-stage voltage boost regulator. Thereby, the harmonic interference due to frequency difference and electromagnetic interference may occur easily.
Therefore, there is an eager demand for a novel cool cathode tube control circuit, which may improve above said prior defects so that the abnormality of load does not effect the lighting device and the illuminations of the plurality of lamp tubes may be identical.
Accordingly, the primary object of the present invention is to provide a cool cathode tube control circuit, wherein the cool cathode tube control circuit includes a regulator control circuit, a lighting control circuit, a fine-adjusting control circuit, and an abnormality detecting circuit for receiving the signals of a fine-adjusting setting circuit and the abnormality protecting circuit and processing the received signals to output digital signals for driving the pre-stage voltage boost regulator and the output the lighting circuit of a lighting device.
Another object of the present invention is to provide a cool cathode tube control circuit, wherein the regulator control circuit can control the pre-stage voltage boost regulator so as to provide a steady high voltage D.C. source.
Another object of the present invention is to provide a cool cathode tube control circuit, wherein in the lighting circuit, the lighting circuit generates various signals through a plurality of voltage shift converters for determining the cutting off and conduction of a power transistor so as to compensate the temperature to the response of the natural resonant variation and to the response of the current variation of the lamp tube. Furthermore, a plurality of lamp tubes can be driven synchronously and the illumination thereof can be adjusted so that they have the same illumination.
Another object of the present invention is to provide a cool cathode tube control circuit, wherein the pre-stage voltage boost regulator is synchronized with the light frequency of the lighting control circuit so as to reduce the interference of the harmonic of the difference frequency and the electromagnetic wave interference.
Another object of the present invention is to provide a cool cathode tube control circuit, wherein the abnormality detecting circuit may track and correct the lighting device immediately by detecting the abnormality of the lighting device through voltage feedback.
Another object of the present invention is to provide a cool cathode tube control circuit, wherein the fine-adjusting control circuit converts the analog illumination adjusting instruction, temperature setting instruction, on/off instruction of the analog protecting circuit and the base voltage adjusting instruction of the voltage regulator into digital signals for being used in the operation of the control logic circuit.